1. Field of the Invention
The present invention relates to a seat reclining apparatus for adjustment of the seatback angle of a reclining seat.
2. Description of Related Art
Japanese Unexamined Patent Publication No. 2012-51466 discloses a known seat reclining apparatus which includes a base plate which is fixed to a seat cushion side frame, a ratchet plate (ratchet) which is fixed to a seatback side frame and provided on the inner periphery thereof with an annular internal gear, a rotational center shaft (hand-operated shaft) for the base plate and the ratchet plate, three lock members (pawls) which are supported on an inner side of the base plate (a surface of the base plate which faces the ratchet plate) thereby to be movable (slidable) relative to the base plate in radial directions of the rotational center shaft, a rotational cam which rotates with the rotational center shaft, and a lock spring (spiral spring) which biases and rotates the rotational center shaft.
An outer toothed portion is formed on an outer peripheral surface of each lock member. Each lock member is movable relative to the base plate (the associated guide groove) between an engaged position in which the outer toothed portion is engaged with the internal gear of the ratchet plate and a disengaged position in which the outer toothed portion is disengaged radially inwards from the internal gear of the ratchet plate.
The rotational cam is rotatable between a locked position, to position each lock member in the engaged position, and an unlocked position, to position each lock member in the disengaged position. The lock spring biases the rotational center shaft in a direction so as to rotate the rotational cam toward the locked position.
Welding protrusions are projected from an outer side of the base plate (a surface of the base plate which faces the seat cushion side frame). The welding protrusions can be engaged in a holding portion which is formed in the seat cushion side frame as a through-hole (note that neither the seat cushion frame nor the holding portion is disclosed in Japanese Unexamined Patent Publication No. 2012-51466). The welding protrusions are fixed to the seat cushion side frame by welding an outer peripheral edge of each welding protrusion to the seat cushion side frame (an outer edge of the holding portion).
When an operating lever (hand-operated lever) which is linked with the rotational center shaft is not manually rotated, the rotational cam rotates toward the locked position by the rotational biasing force of the lock spring, which causes each lock member to move toward the engaged position. Accordingly, the outer toothed portion of each lock member is engaged with the internal gear of the ratchet plate, so that the seatback side frame (seatback) becomes non-rotatable relative to the seat cushion side frame (seat cushion).
On the other hand, the operating lever is manually rotated against the rotational biasing force of the lock spring, the rotational cam moves to the unlocked position. Thereupon, each lock member having moved to the engaged position moves toward the disengaged position, which causes the outer toothed portion of each lock member to be disengaged from the internal gear of the ratchet plate. As a result, the seatback side frame (seatback) becomes rotatable relative to the seat cushion side frame (seat cushion) (i.e., the angle of the seatback becomes adjustable relative to the seat cushion).
The aforementioned welding protrusions of the seat reclining apparatus disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 2012-51466 are positioned closer to the center of the base plate (closer to the inner peripheral side of the base plate) than the outer toothed portion (the outer periphery) of each lock member in the engaged position.
If welding is applied so as to extend over an outer peripheral edge of each welding protrusion and the seat cushion side frame (an outer edge of the aforementioned holding portion of the seat cushion side frame), heat caused by welding reaches the inner side of the base plate through the inside of the base plate. Consequently, this heat eventually reaches the lock member support portion on the inner side of the base plate because the welding protrusions are positioned closer to the center of the base plate (closer to the inner peripheral side of the base plate) than the outer toothed portion (the outer periphery) of each lock member in the engaged position.
Thereupon, the lock member support portion of the base plate (the inner side of the base plate) may be deformed (e.g., deformed to bulge toward the lock member) by the aforementioned heat caused by welding, so that each lock member may become incapable of sliding smoothly on the inner side (the lock member support portion) of the base plate.